The present invention relates to a method and apparatus for reducing the size of an image buffer in a color printer, and more particularly, to intelligent doubling of scaled images, wherein smooth areas of an image are distinguished from edges and are scaled differently. The invention provides scaling methods for the encodings used in the split-level image buffer and further encodings useful for graphics and text.
Modern page description languages describe a page as a sequence of primitive drawing commands. The full page image is constructed by executing these commands and collecting the image elements they produce. Printers form an internal representation of the desired page in a computer memory prior to marking. The memory is called the image buffer and typically contains a color value for every spot or pixel that can be marked. The page can have a large number of pixels (e.g. 90,000 to 360,000 per square inch) and so a great deal of memory is typically required for the image buffer.
U.S. Pat. No. 5,276,532 entitled "Split-Level Frame Buffer" describes a method to reduce the amount of memory required to construct a full color page image for printing. The method encodes the page images using two resolutions, a low resolution for object interiors and a high resolution for object edges. This patent application is herein incorporated by reference. Subsequent inventions provide efficient encodings of the high resolution edge pixels for two-color patterns, edges separating two colors and ordered regions of three colors. Line graphics and scanned pictorial images can be expressed using these encodings resulting in a compression (or reduction of the memory requirements) of up to 16 to 1.